1. Field of the Invention
The present invention relates to a lighting fixture used as a navigational aid, using light-emitting diodes (LEDs) having different divergence angles in the horizontal and perpendicular directions, i.e., a so-called elliptic light distribution, as the light source.
2. Prior Art
LEDs are widely used as light sources in navigational aids on account of their low power consumption and low failure rate.
Because the light-emitting energy of a single LED is small, a tubular lens is typically used to surround several LEDs in order to concentrate their light by convergence, thereby increasing their effective illumination. However, if LEDs with a high convergence rate are arranged in a large array, their light is not distributed uniformly in the horizontal circumferential direction, which is how the light should ideally be distributed. Therefore, in order to distribute the light horizontally and uniformly, LEDs with a wider divergence angle have been used conventionally.
Typically the divergence angle is 30° or so for both the horizontal divergence angle and the perpendicular divergence angle. To make the horizontal light distribution more nearly concentric, a multitude of LEDs need to be arranged horizontally. In some cases, as many as 80 LEDs are arranged in a row.
Since typical lighting fixtures for navigational aid purposes use several tiers of LEDs, the total number of LEDs used in a lighting fixture can be very large.
As the number of LEDs per tier increases, the outer diameter of the substrate on which the LEDs are mounted also needs to be increased, with the result that the outer diameter of the lighting fixture has to be made larger.